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Strain Measurement techniques for pipelines Disclosure Number: IPCOM000200915D
Publication Date: 2010-Oct-29
Document File: 2 page(s) / 27K

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Techniques aimed at obtaining measurements of pipeline membrane strains through instrumented pigs are discussed

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This is the abbreviated version, containing approximately 53% of the total text.

Strain Measurement techniques for pipelines

Technical Memorandum,  18 June 2010

The following techniques aim at obtaining accurate measurements of pipeline strains through instrumented pigs. Although it is possible to estimate bending strains from pipeline curvature, such measurements do not account for membrane strains that may be important contributors under certain loading conditions. The following solutions address this shortcoming (it should be noted that all techniques may be applied externally as well, but would then require exposure for monitoring):

Description of different techniques

Technique 1: Use strain-sensitive polymer coating on the inside of the pipe

a) Apply a polymer coating that changes color, transparency or conductivity as it strains. Depending on the control over the property and thickness of the polymer, the coating could either provide a graduated strain measurement or simply a binary reading (predefined strain exceeded or not). Many polymers whiten under strain and could be suitable for this system. Other polymers exhibit alternative monitorable changes with strains (conductivity, piezoresistivity, etc.) Note that this polymer could be used in place of an internal flow coating. Alternatively, such a coating could be engineered to provide this property.

Technique 2: Use a brittle polymer coating on the inside of the pipe

A brittle polymer coating (such as a lacquer) could be applied to the inside of the pipe. Such polymers exhibit cracking under strain, the level of cracking increasing with the level of strain. Different options are available to 'read' the strain by monitoring variations in properties of the polymer: polymer color read by optical devices, polymer resistivity / conductivity read by contacts on the pig; polymer capacitance read by a sensor on the pig, etc.

Technique 3: Paint a ring with a well defined width on the inside of the pipe

Simple photo-diodes could be used during pigging to measure variations in width of an initially well defined painted ring. Measurements of the ring width at several locations arou...